GCVE Workshop - 22 September 2026 (14:00-18:00), Luxembourg Before The Vulnopticon Conference - Registration

CVE-2026-63073 (GCVE-0-2026-63073)

Vulnerability from cvelistv5 – Published: 2026-08-25 12:59 – Updated: 2026-08-31 19:12
VLAI
Title
Untrusted Sender DN Used as Format String in CMP Response Validation
Summary
Issue summary: OpenSSL CMP response validation passed an unexpected response sender distinguished name directly as the format string to `ERR_raise_data()`. Impact summary: A malicious or intercepted CMP endpoint can crash a CMP client that enforces an expected sender or uses a pinned server certificate whose subject becomes the default expected sender. CWE: CWE-134 (Use of Externally-Controlled Format String) Description: When validating a received CMP message, ossl_cmp_msg_check_update() converts the peer-supplied sender distinguished name with X509_NAME_oneline() and passes it directly as the format argument to ERR_raise_data(). Percent characters survive the conversion, so a sender DN such as "CN=%s%n" reaches BIO_vsnprintf() as an attacker-controlled format string with no matching variadic arguments. This path is only reached when the caller configures an expected sender or pins a server certificate, which is the normal configuration for a CMP client validating server responses. Since the attacker controls the format string but none of the variadic arguments, such specifiers as %s and %n dereference or write through unrelated stack contents and crash the client. The reliable consequence is a denial of service, when the response comes from a malicious or intercepted CMP endpoint. There is no controlled memory write, arbitrary-address read, or reliable path to remote code execution. FIPS impact: no No FIPS modules are affected by this issue, as the CMP protocol implementation is outside the OpenSSL FIPS module boundary.
Severity
9.8 (Critical)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
SSVC
Exploitation: none Automatable: yes Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-08-31 19:12 UTC
CWE
  • CWE-134 - Use of Externally-Controlled Format String
Assigner
References
Impacted products
Vendor Product Version CPE status
OpenSSL OpenSSL Affected: 4.0.0 , < 4.0.2 (semver)
Affected: 3.6.0 , < 3.6.4 (semver)
Affected: 3.5.0 , < 3.5.8 (semver)
Affected: 3.4.0 , < 3.4.7 (semver)
guessed Create a notification for this product.
Date Public
2026-08-25 11:36
Credits
Filipe Casal (Trail of Bits) Brandon Luo TrendAI Zero Day Initiative Filipe Casal (Trail of Bits)
Show details on NVD website
To clipboard 

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "cvssV3_1": {
              "attackComplexity": "LOW",
              "attackVector": "NETWORK",
              "availabilityImpact": "HIGH",
              "baseScore": 9.8,
              "baseSeverity": "CRITICAL",
              "confidentialityImpact": "HIGH",
              "integrityImpact": "HIGH",
              "privilegesRequired": "NONE",
              "scope": "UNCHANGED",
              "userInteraction": "NONE",
              "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
              "version": "3.1"
            }
          },
          {
            "other": {
              "content": {
                "id": "CVE-2026-63073",
                "options": [
                  {
                    "Exploitation": "none"
                  },
                  {
                    "Automatable": "yes"
                  },
                  {
                    "Technical Impact": "total"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-08-31T19:12:48.434586Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2026-08-31T19:12:54.136Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "OpenSSL",
          "vendor": "OpenSSL",
          "versions": [
            {
              "lessThan": "4.0.2",
              "status": "affected",
              "version": "4.0.0",
              "versionType": "semver"
            },
            {
              "lessThan": "3.6.4",
              "status": "affected",
              "version": "3.6.0",
              "versionType": "semver"
            },
            {
              "lessThan": "3.5.8",
              "status": "affected",
              "version": "3.5.0",
              "versionType": "semver"
            },
            {
              "lessThan": "3.4.7",
              "status": "affected",
              "version": "3.4.0",
              "versionType": "semver"
            }
          ]
        }
      ],
      "credits": [
        {
          "lang": "en",
          "type": "reporter",
          "value": "Filipe Casal (Trail of Bits)"
        },
        {
          "lang": "en",
          "type": "reporter",
          "value": "Brandon Luo"
        },
        {
          "lang": "en",
          "type": "reporter",
          "value": "TrendAI Zero Day Initiative"
        },
        {
          "lang": "en",
          "type": "remediation developer",
          "value": "Filipe Casal (Trail of Bits)"
        }
      ],
      "datePublic": "2026-08-25T11:36:16.000Z",
      "descriptions": [
        {
          "lang": "en",
          "supportingMedia": [
            {
              "base64": false,
              "type": "text/html",
              "value": "Issue summary: OpenSSL CMP response validation passed an unexpected response\u003cbr\u003esender distinguished name directly as the format string to `ERR_raise_data()`.\u003cbr\u003e\u003cbr\u003eImpact summary: A malicious or intercepted CMP endpoint can crash a CMP client\u003cbr\u003ethat enforces an expected sender or uses a pinned server certificate whose\u003cbr\u003esubject becomes the default expected sender.\u003cbr\u003e\u003cbr\u003eCWE: CWE-134 (Use of Externally-Controlled Format String)\u003cbr\u003e\u003cbr\u003eDescription: When validating a received CMP message, ossl_cmp_msg_check_update()\u003cbr\u003econverts the peer-supplied sender distinguished name with X509_NAME_oneline()\u003cbr\u003eand passes it directly as the format argument to ERR_raise_data(). Percent\u003cbr\u003echaracters survive the conversion, so a sender DN such as \"CN=%s%n\" reaches\u003cbr\u003eBIO_vsnprintf() as an attacker-controlled format string with no matching variadic\u003cbr\u003earguments. This path is only reached when the caller configures an expected\u003cbr\u003esender or pins a server certificate, which is the normal configuration for a\u003cbr\u003eCMP client validating server responses.\u003cbr\u003e\u003cbr\u003eSince the attacker controls the format string but none of the variadic\u003cbr\u003earguments, such specifiers as %s and %n dereference or write through unrelated\u003cbr\u003estack contents and crash the client. The reliable consequence is a denial of\u003cbr\u003eservice, when the response comes from a malicious or intercepted CMP endpoint.\u003cbr\u003eThere is no controlled memory write, arbitrary-address read, or reliable path\u003cbr\u003eto remote code execution.\u003cbr\u003e\u003cbr\u003eFIPS impact: no\u003cbr\u003e\u003cbr\u003eNo FIPS modules are affected by this issue, as the CMP protocol\u003cbr\u003eimplementation is outside the OpenSSL FIPS module boundary."
            }
          ],
          "value": "Issue summary: OpenSSL CMP response validation passed an unexpected response\nsender distinguished name directly as the format string to `ERR_raise_data()`.\n\nImpact summary: A malicious or intercepted CMP endpoint can crash a CMP client\nthat enforces an expected sender or uses a pinned server certificate whose\nsubject becomes the default expected sender.\n\nCWE: CWE-134 (Use of Externally-Controlled Format String)\n\nDescription: When validating a received CMP message, ossl_cmp_msg_check_update()\nconverts the peer-supplied sender distinguished name with X509_NAME_oneline()\nand passes it directly as the format argument to ERR_raise_data(). Percent\ncharacters survive the conversion, so a sender DN such as \"CN=%s%n\" reaches\nBIO_vsnprintf() as an attacker-controlled format string with no matching variadic\narguments. This path is only reached when the caller configures an expected\nsender or pins a server certificate, which is the normal configuration for a\nCMP client validating server responses.\n\nSince the attacker controls the format string but none of the variadic\narguments, such specifiers as %s and %n dereference or write through unrelated\nstack contents and crash the client. The reliable consequence is a denial of\nservice, when the response comes from a malicious or intercepted CMP endpoint.\nThere is no controlled memory write, arbitrary-address read, or reliable path\nto remote code execution.\n\nFIPS impact: no\n\nNo FIPS modules are affected by this issue, as the CMP protocol\nimplementation is outside the OpenSSL FIPS module boundary."
        }
      ],
      "metrics": [
        {
          "format": "other",
          "other": {
            "content": {
              "text": "Low"
            },
            "type": "https://openssl-library.org/policies/general/security-policy/"
          }
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-134",
              "description": "Use of Externally-Controlled Format String",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-25T12:59:43.356Z",
        "orgId": "3a12439a-ef3a-4c79-92e6-6081a721f1e5",
        "shortName": "openssl"
      },
      "references": [
        {
          "name": "OpenSSL Advisory",
          "tags": [
            "vendor-advisory"
          ],
          "url": "https://openssl-library.org/news/secadv/20260825.txt"
        },
        {
          "name": "4.0.2 git commit",
          "tags": [
            "patch"
          ],
          "url": "https://github.com/openssl/openssl/commit/7eb2e3ec9d1d4f35c8022fccd4b03398b3f33e21"
        },
        {
          "name": "3.6.4 git commit",
          "tags": [
            "patch"
          ],
          "url": "https://github.com/openssl/openssl/commit/6a0acc072b4d37a7cac1252a29c1ce1f00c5ec29"
        },
        {
          "name": "3.5.8 git commit",
          "tags": [
            "patch"
          ],
          "url": "https://github.com/openssl/openssl/commit/0cc20b322639919aa423e90799d9a57c3b4b76ca"
        },
        {
          "name": "3.4.7 git commit",
          "tags": [
            "patch"
          ],
          "url": "https://github.com/openssl/openssl/commit/a7e5a6eea8fd3ccca6b6fbba031a5fbf8a3d93b4"
        }
      ],
      "source": {
        "discovery": "UNKNOWN"
      },
      "title": "Untrusted Sender DN Used as Format String in CMP Response Validation",
      "x_generator": {
        "engine": "Vulnogram 0.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "3a12439a-ef3a-4c79-92e6-6081a721f1e5",
    "assignerShortName": "openssl",
    "cveId": "CVE-2026-63073",
    "datePublished": "2026-08-25T12:59:43.356Z",
    "dateReserved": "2026-07-15T13:10:26.188Z",
    "dateUpdated": "2026-08-31T19:12:54.136Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "epss": {
      "cve": "CVE-2026-63073",
      "date": "2026-09-16",
      "epss": "0.00929",
      "percentile": "0.58832"
    },
    "microsoft_vex": {
      "current_release_date": "2026-09-13T01:50:52.000Z",
      "cve": "CVE-2026-63073",
      "id": "msrc_CVE-2026-63073",
      "initial_release_date": "2026-08-27T01:12:28.000Z",
      "product_status:fixed": "1",
      "product_status:known_affected": "6",
      "product_status:known_not_affected": "1",
      "source": "Microsoft CSAF VEX",
      "status": "final",
      "title": "Untrusted Sender DN Used as Format String in CMP Response Validation",
      "url": "https://msrc.microsoft.com/csaf/vex/2026/msrc_cve-2026-63073.json",
      "version": "5"
    },
    "nvd": "{\"cve\":{\"id\":\"CVE-2026-63073\",\"sourceIdentifier\":\"openssl-security@openssl.org\",\"published\":\"2026-08-25T13:19:26.147\",\"lastModified\":\"2026-09-11T21:16:45.633\",\"vulnStatus\":\"Analyzed\",\"cveTags\":[],\"descriptions\":[{\"lang\":\"en\",\"value\":\"Issue summary: OpenSSL CMP response validation passed an unexpected response\\nsender distinguished name directly as the format string to `ERR_raise_data()`.\\n\\nImpact summary: A malicious or intercepted CMP endpoint can crash a CMP client\\nthat enforces an expected sender or uses a pinned server certificate whose\\nsubject becomes the default expected sender.\\n\\nCWE: CWE-134 (Use of Externally-Controlled Format String)\\n\\nDescription: When validating a received CMP message, ossl_cmp_msg_check_update()\\nconverts the peer-supplied sender distinguished name with X509_NAME_oneline()\\nand passes it directly as the format argument to ERR_raise_data(). Percent\\ncharacters survive the conversion, so a sender DN such as \\\"CN=%s%n\\\" reaches\\nBIO_vsnprintf() as an attacker-controlled format string with no matching variadic\\narguments. This path is only reached when the caller configures an expected\\nsender or pins a server certificate, which is the normal configuration for a\\nCMP client validating server responses.\\n\\nSince the attacker controls the format string but none of the variadic\\narguments, such specifiers as %s and %n dereference or write through unrelated\\nstack contents and crash the client. The reliable consequence is a denial of\\nservice, when the response comes from a malicious or intercepted CMP endpoint.\\nThere is no controlled memory write, arbitrary-address read, or reliable path\\nto remote code execution.\\n\\nFIPS impact: no\\n\\nNo FIPS modules are affected by this issue, as the CMP protocol\\nimplementation is outside the OpenSSL FIPS module boundary.\"}],\"affected\":[{\"source\":\"openssl-security@openssl.org\",\"affectedData\":[{\"vendor\":\"OpenSSL\",\"product\":\"OpenSSL\",\"defaultStatus\":\"unaffected\",\"versions\":[{\"version\":\"4.0.0\",\"lessThan\":\"4.0.2\",\"versionType\":\"semver\",\"status\":\"affected\"},{\"version\":\"3.6.0\",\"lessThan\":\"3.6.4\",\"versionType\":\"semver\",\"status\":\"affected\"},{\"version\":\"3.5.0\",\"lessThan\":\"3.5.8\",\"versionType\":\"semver\",\"status\":\"affected\"},{\"version\":\"3.4.0\",\"lessThan\":\"3.4.7\",\"versionType\":\"semver\",\"status\":\"affected\"}]}]}],\"metrics\":{\"cvssMetricV31\":[{\"source\":\"134c704f-9b21-4f2e-91b3-4a467353bcc0\",\"type\":\"Secondary\",\"cvssData\":{\"version\":\"3.1\",\"vectorString\":\"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H\",\"baseScore\":9.8,\"baseSeverity\":\"CRITICAL\",\"attackVector\":\"NETWORK\",\"attackComplexity\":\"LOW\",\"privilegesRequired\":\"NONE\",\"userInteraction\":\"NONE\",\"scope\":\"UNCHANGED\",\"confidentialityImpact\":\"HIGH\",\"integrityImpact\":\"HIGH\",\"availabilityImpact\":\"HIGH\"},\"exploitabilityScore\":3.9,\"impactScore\":5.9}],\"ssvcV203\":[{\"source\":\"134c704f-9b21-4f2e-91b3-4a467353bcc0\",\"ssvcData\":{\"timestamp\":\"2026-08-31T19:12:48.434586Z\",\"id\":\"CVE-2026-63073\",\"options\":[{\"exploitation\":\"none\"},{\"automatable\":\"yes\"},{\"technicalImpact\":\"total\"}],\"role\":\"CISA Coordinator\",\"version\":\"2.0.3\"}}]},\"weaknesses\":[{\"source\":\"openssl-security@openssl.org\",\"type\":\"Secondary\",\"description\":[{\"lang\":\"en\",\"value\":\"CWE-134\"}]}],\"configurations\":[{\"nodes\":[{\"operator\":\"OR\",\"negate\":false,\"cpeMatch\":[{\"vulnerable\":true,\"criteria\":\"cpe:2.3:a:openssl:openssl:*:*:*:*:*:*:*:*\",\"versionStartIncluding\":\"3.4.0\",\"versionEndExcluding\":\"3.4.7\",\"matchCriteriaId\":\"216D6529-561A-4684-A886-50954FBEBFB2\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:a:openssl:openssl:*:*:*:*:*:*:*:*\",\"versionStartIncluding\":\"3.5.0\",\"versionEndExcluding\":\"3.5.8\",\"matchCriteriaId\":\"C5BB9E95-09B6-4163-B51C-D62B528A04DA\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:a:openssl:openssl:*:*:*:*:*:*:*:*\",\"versionStartIncluding\":\"3.6.0\",\"versionEndExcluding\":\"3.6.4\",\"matchCriteriaId\":\"B1416826-F2F1-4EA8-9FB2-A56B0DA923C1\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:a:openssl:openssl:*:*:*:*:*:*:*:*\",\"versionStartIncluding\":\"4.0.0\",\"versionEndExcluding\":\"4.0.2\",\"matchCriteriaId\":\"63B8F45B-E44F-481C-815D-AF9CA89C48F6\"}]}]}],\"references\":[{\"url\":\"https://github.com/openssl/openssl/commit/0cc20b322639919aa423e90799d9a57c3b4b76ca\",\"source\":\"openssl-security@openssl.org\",\"tags\":[\"Patch\"]},{\"url\":\"https://github.com/openssl/openssl/commit/6a0acc072b4d37a7cac1252a29c1ce1f00c5ec29\",\"source\":\"openssl-security@openssl.org\",\"tags\":[\"Patch\"]},{\"url\":\"https://github.com/openssl/openssl/commit/7eb2e3ec9d1d4f35c8022fccd4b03398b3f33e21\",\"source\":\"openssl-security@openssl.org\",\"tags\":[\"Patch\"]},{\"url\":\"https://github.com/openssl/openssl/commit/a7e5a6eea8fd3ccca6b6fbba031a5fbf8a3d93b4\",\"source\":\"openssl-security@openssl.org\",\"tags\":[\"Patch\"]},{\"url\":\"https://openssl-library.org/news/secadv/20260825.txt\",\"source\":\"openssl-security@openssl.org\",\"tags\":[\"Vendor Advisory\"]}]}}",
    "redhat_vex": {
      "aggregate_severity": "Low",
      "current_release_date": "2026-09-14T07:59:11+00:00",
      "cve": "CVE-2026-63073",
      "id": "CVE-2026-63073",
      "initial_release_date": "2026-08-25T00:00:00+00:00",
      "product_status:fixed": "96",
      "product_status:known_affected": "16",
      "product_status:known_not_affected": "66",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "openssl: untrusted sender DN used as format string in CMP response validation",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-63073.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "moderate",
      "current_release_date": "2026-09-15T01:59:59Z",
      "cve": "CVE-2026-63073",
      "id": "CVE-2026-63073",
      "initial_release_date": "2026-08-28T01:06:09Z",
      "product_status:known_affected": "394",
      "product_status:known_not_affected": "562",
      "product_status:recommended": "59",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-63073",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-63073.json",
      "version": "10"
    },
    "vulnrichment": {
      "containers": "{\"adp\": [{\"title\": \"CISA ADP Vulnrichment\", \"metrics\": [{\"cvssV3_1\": {\"scope\": \"UNCHANGED\", \"version\": \"3.1\", \"baseScore\": 9.8, \"attackVector\": \"NETWORK\", \"baseSeverity\": \"CRITICAL\", \"vectorString\": \"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H\", \"integrityImpact\": \"HIGH\", \"userInteraction\": \"NONE\", \"attackComplexity\": \"LOW\", \"availabilityImpact\": \"HIGH\", \"privilegesRequired\": \"NONE\", \"confidentialityImpact\": \"HIGH\"}}, {\"other\": {\"type\": \"ssvc\", \"content\": {\"id\": \"CVE-2026-63073\", \"role\": \"CISA Coordinator\", \"options\": [{\"Exploitation\": \"none\"}, {\"Automatable\": \"yes\"}, {\"Technical Impact\": \"total\"}], \"version\": \"2.0.3\", \"timestamp\": \"2026-08-31T19:12:48.434586Z\"}}}], \"providerMetadata\": {\"orgId\": \"134c704f-9b21-4f2e-91b3-4a467353bcc0\", \"shortName\": \"CISA-ADP\", \"dateUpdated\": \"2026-08-31T19:12:32.854Z\"}}], \"cna\": {\"title\": \"Untrusted Sender DN Used as Format String in CMP Response Validation\", \"source\": {\"discovery\": \"UNKNOWN\"}, \"credits\": [{\"lang\": \"en\", \"type\": \"reporter\", \"value\": \"Filipe Casal (Trail of Bits)\"}, {\"lang\": \"en\", \"type\": \"reporter\", \"value\": \"Brandon Luo\"}, {\"lang\": \"en\", \"type\": \"reporter\", \"value\": \"TrendAI Zero Day Initiative\"}, {\"lang\": \"en\", \"type\": \"remediation developer\", \"value\": \"Filipe Casal (Trail of Bits)\"}], \"metrics\": [{\"other\": {\"type\": \"https://openssl-library.org/policies/general/security-policy/\", \"content\": {\"text\": \"Low\"}}, \"format\": \"other\"}], \"affected\": [{\"vendor\": \"OpenSSL\", \"product\": \"OpenSSL\", \"versions\": [{\"status\": \"affected\", \"version\": \"4.0.0\", \"lessThan\": \"4.0.2\", \"versionType\": \"semver\"}, {\"status\": \"affected\", \"version\": \"3.6.0\", \"lessThan\": \"3.6.4\", \"versionType\": \"semver\"}, {\"status\": \"affected\", \"version\": \"3.5.0\", \"lessThan\": \"3.5.8\", \"versionType\": \"semver\"}, {\"status\": \"affected\", \"version\": \"3.4.0\", \"lessThan\": \"3.4.7\", \"versionType\": \"semver\"}], \"defaultStatus\": \"unaffected\"}], \"datePublic\": \"2026-08-25T11:36:16.000Z\", \"references\": [{\"url\": \"https://openssl-library.org/news/secadv/20260825.txt\", \"name\": \"OpenSSL Advisory\", \"tags\": [\"vendor-advisory\"]}, {\"url\": \"https://github.com/openssl/openssl/commit/7eb2e3ec9d1d4f35c8022fccd4b03398b3f33e21\", \"name\": \"4.0.2 git commit\", \"tags\": [\"patch\"]}, {\"url\": \"https://github.com/openssl/openssl/commit/6a0acc072b4d37a7cac1252a29c1ce1f00c5ec29\", \"name\": \"3.6.4 git commit\", \"tags\": [\"patch\"]}, {\"url\": \"https://github.com/openssl/openssl/commit/0cc20b322639919aa423e90799d9a57c3b4b76ca\", \"name\": \"3.5.8 git commit\", \"tags\": [\"patch\"]}, {\"url\": \"https://github.com/openssl/openssl/commit/a7e5a6eea8fd3ccca6b6fbba031a5fbf8a3d93b4\", \"name\": \"3.4.7 git commit\", \"tags\": [\"patch\"]}], \"x_generator\": {\"engine\": \"Vulnogram 0.2.0\"}, \"descriptions\": [{\"lang\": \"en\", \"value\": \"Issue summary: OpenSSL CMP response validation passed an unexpected response\\nsender distinguished name directly as the format string to `ERR_raise_data()`.\\n\\nImpact summary: A malicious or intercepted CMP endpoint can crash a CMP client\\nthat enforces an expected sender or uses a pinned server certificate whose\\nsubject becomes the default expected sender.\\n\\nCWE: CWE-134 (Use of Externally-Controlled Format String)\\n\\nDescription: When validating a received CMP message, ossl_cmp_msg_check_update()\\nconverts the peer-supplied sender distinguished name with X509_NAME_oneline()\\nand passes it directly as the format argument to ERR_raise_data(). Percent\\ncharacters survive the conversion, so a sender DN such as \\\"CN=%s%n\\\" reaches\\nBIO_vsnprintf() as an attacker-controlled format string with no matching variadic\\narguments. This path is only reached when the caller configures an expected\\nsender or pins a server certificate, which is the normal configuration for a\\nCMP client validating server responses.\\n\\nSince the attacker controls the format string but none of the variadic\\narguments, such specifiers as %s and %n dereference or write through unrelated\\nstack contents and crash the client. The reliable consequence is a denial of\\nservice, when the response comes from a malicious or intercepted CMP endpoint.\\nThere is no controlled memory write, arbitrary-address read, or reliable path\\nto remote code execution.\\n\\nFIPS impact: no\\n\\nNo FIPS modules are affected by this issue, as the CMP protocol\\nimplementation is outside the OpenSSL FIPS module boundary.\", \"supportingMedia\": [{\"type\": \"text/html\", \"value\": \"Issue summary: OpenSSL CMP response validation passed an unexpected response\u003cbr\u003esender distinguished name directly as the format string to `ERR_raise_data()`.\u003cbr\u003e\u003cbr\u003eImpact summary: A malicious or intercepted CMP endpoint can crash a CMP client\u003cbr\u003ethat enforces an expected sender or uses a pinned server certificate whose\u003cbr\u003esubject becomes the default expected sender.\u003cbr\u003e\u003cbr\u003eCWE: CWE-134 (Use of Externally-Controlled Format String)\u003cbr\u003e\u003cbr\u003eDescription: When validating a received CMP message, ossl_cmp_msg_check_update()\u003cbr\u003econverts the peer-supplied sender distinguished name with X509_NAME_oneline()\u003cbr\u003eand passes it directly as the format argument to ERR_raise_data(). Percent\u003cbr\u003echaracters survive the conversion, so a sender DN such as \\\"CN=%s%n\\\" reaches\u003cbr\u003eBIO_vsnprintf() as an attacker-controlled format string with no matching variadic\u003cbr\u003earguments. This path is only reached when the caller configures an expected\u003cbr\u003esender or pins a server certificate, which is the normal configuration for a\u003cbr\u003eCMP client validating server responses.\u003cbr\u003e\u003cbr\u003eSince the attacker controls the format string but none of the variadic\u003cbr\u003earguments, such specifiers as %s and %n dereference or write through unrelated\u003cbr\u003estack contents and crash the client. The reliable consequence is a denial of\u003cbr\u003eservice, when the response comes from a malicious or intercepted CMP endpoint.\u003cbr\u003eThere is no controlled memory write, arbitrary-address read, or reliable path\u003cbr\u003eto remote code execution.\u003cbr\u003e\u003cbr\u003eFIPS impact: no\u003cbr\u003e\u003cbr\u003eNo FIPS modules are affected by this issue, as the CMP protocol\u003cbr\u003eimplementation is outside the OpenSSL FIPS module boundary.\", \"base64\": false}]}], \"problemTypes\": [{\"descriptions\": [{\"lang\": \"en\", \"type\": \"CWE\", \"cweId\": \"CWE-134\", \"description\": \"Use of Externally-Controlled Format String\"}]}], \"providerMetadata\": {\"orgId\": \"3a12439a-ef3a-4c79-92e6-6081a721f1e5\", \"shortName\": \"openssl\", \"dateUpdated\": \"2026-08-25T12:59:43.356Z\"}}}",
      "cveMetadata": "{\"cveId\": \"CVE-2026-63073\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2026-08-31T19:12:54.136Z\", \"dateReserved\": \"2026-07-15T13:10:26.188Z\", \"assignerOrgId\": \"3a12439a-ef3a-4c79-92e6-6081a721f1e5\", \"datePublished\": \"2026-08-25T12:59:43.356Z\", \"assignerShortName\": \"openssl\"}",
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}



Log in or create an account to share your comment.




Tags
Taxonomy of the tags.





Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

Author Source Type Date Other

Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


Detection rules are retrieved from Rulezet.


Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.